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Kim R, Yu T, Li J, Prochazka J, Sharir A, Green JBA, Klein OD. Early perturbation of Wnt signaling reveals patterning and invagination-evagination control points in molar tooth development. Development 2021; 148:dev199685. [PMID: 34195802 PMCID: PMC8326921 DOI: 10.1242/dev.199685] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Accepted: 06/28/2021] [Indexed: 01/07/2023]
Abstract
Tooth formation requires complex signaling interactions both within the oral epithelium and between the epithelium and the underlying mesenchyme. Previous studies of the Wnt/β-catenin pathway have shown that tooth formation is partly inhibited in loss-of-function mutants, and gain-of-function mutants have perturbed tooth morphology. However, the stage at which Wnt signaling is first important in tooth formation remains unclear. Here, using an Fgf8-promoter-driven, and therefore early, deletion of β-catenin in mouse molar epithelium, we found that loss of Wnt/β-catenin signaling completely deletes the molar tooth, demonstrating that this pathway is central to the earliest stages of tooth formation. Early expression of a dominant-active β-catenin protein also perturbs tooth formation, producing a large domed evagination at early stages and supernumerary teeth later on. The early evaginations are associated with premature mesenchymal condensation marker, and are reduced by inhibition of condensation-associated collagen synthesis. We propose that invagination versus evagination morphogenesis is regulated by the relative timing of epithelial versus mesenchymal cell convergence regulated by canonical Wnt signaling. Together, these studies reveal new aspects of Wnt/β-catenin signaling in tooth formation and in epithelial morphogenesis more broadly.
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Affiliation(s)
- Rebecca Kim
- Program in Craniofacial Biology and Department of Orofacial Sciences, University of California, San Francisco, CA 94143, USA
| | - Tingsheng Yu
- Program in Craniofacial Biology and Department of Orofacial Sciences, University of California, San Francisco, CA 94143, USA
| | - Jingjing Li
- Centre for Craniofacial Regeneration and Biology, King's College London, London, SE1 9RT, UK
| | - Jan Prochazka
- Institute of Molecular Genetics of the ASCR, v. v. i., Prumyslova 595, 252 42 Vestec, Czech Republic
| | - Amnon Sharir
- Program in Craniofacial Biology and Department of Orofacial Sciences, University of California, San Francisco, CA 94143, USA
| | - Jeremy B. A. Green
- Program in Craniofacial Biology and Department of Orofacial Sciences, University of California, San Francisco, CA 94143, USA
- Centre for Craniofacial Regeneration and Biology, King's College London, London, SE1 9RT, UK
| | - Ophir D. Klein
- Program in Craniofacial Biology and Department of Orofacial Sciences, University of California, San Francisco, CA 94143, USA
- Department of Pediatrics and Institute for Human Genetics, University of California, San Francisco, CA 94143, USA
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Brink KS, Henríquez JI, Grieco TM, Martin del Campo JR, Fu K, Richman JM. Tooth Removal in the Leopard Gecko and the de novo Formation of Replacement Teeth. Front Physiol 2021; 12:576816. [PMID: 34012403 PMCID: PMC8126719 DOI: 10.3389/fphys.2021.576816] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 03/25/2021] [Indexed: 11/13/2022] Open
Abstract
Many reptiles are able to continuously replace their teeth through life, an ability attributed to the existence of epithelial stem cells. Tooth replacement occurs in a spatially and temporally regulated manner, suggesting the involvement of diffusible factors, potentially over long distances. Here, we locally disrupted tooth replacement in the leopard gecko (Eublepharis macularius) and followed the recovery of the dentition. We looked at the effects on local patterning and functionally tested whether putative epithelial stem cells can give rise to multiple cell types in the enamel organs of new teeth. Second generation teeth with enamel and dentine were removed from adult geckos. The dental lamina was either left intact or disrupted in order to interfere with local patterning cues. The dentition began to reform by 1 month and was nearly recovered by 2-3 months as shown in μCT scans and eruption of teeth labeled with fluorescent markers. Microscopic analysis showed that the dental lamina was fully healed by 1 month. The deepest parts of the dental lamina retained odontogenic identity as shown by PITX2 staining. A pulse-chase was carried out to label cells that were stimulated to enter the cell cycle and then would carry BrdU forward into subsequent tooth generations. Initially we labeled 70-78% of PCNA cells with BrdU. After a 1-month chase, the percentage of BrdU + PCNA labeled cells in the dental lamina had dropped to 10%, consistent with the dilution of the label. There was also a population of single, BrdU-labeled cells present up to 2 months post surgery. These BrdU-labeled cells were almost entirely located in the dental lamina and were the likely progenitor/stem cells because they had not entered the cell cycle. In contrast fragmented BrdU was seen in the PCNA-positive, proliferating enamel organs. Homeostasis and recovery of the gecko dentition was therefore mediated by a stable population of epithelial stem cells in the dental lamina.
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Affiliation(s)
| | | | | | | | | | - Joy M. Richman
- Department of Oral Health Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
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Brink KS, Wu P, Chuong CM, Richman JM. The Effects of Premature Tooth Extraction and Damage on Replacement Timing in the Green Iguana. Integr Comp Biol 2020; 60:581-593. [PMID: 32974642 PMCID: PMC7546963 DOI: 10.1093/icb/icaa099] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Reptiles with continuous tooth replacement, or polyphyodonty, replace their teeth in predictable, well-timed waves in alternating tooth positions around the mouth. This process is thought to occur irrespective of tooth wear or breakage. In this study, we aimed to determine if damage to teeth and premature tooth extraction affects tooth replacement timing long-term in juvenile green iguanas (Iguana iguana). First, we examined normal tooth development histologically using a BrdU pulse-chase analysis to detect label-retaining cells in replacement teeth and dental tissues. Next, we performed tooth extraction experiments for characterization of dental tissues after functional tooth (FT) extraction, including proliferation and β-Catenin expression, for up to 12 weeks. We then compared these results to a newly analyzed historical dataset of X-rays collected up to 7 months after FT damage and extraction in the green iguana. Results show that proliferation in the dental and successional lamina (SL) does not change after extraction of the FT, and proliferation occurs in the SL only when a tooth differentiates. Damage to an FT crown does not affect the timing of the tooth replacement cycle, however, complete extraction shifts the replacement cycle ahead by 4 weeks by removing the need for resorption of the FT. These results suggest that traumatic FT loss affects the timing of the replacement cycle at that one position, which may have implications for tooth replacement patterning around the entire mouth.
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Affiliation(s)
- Kirstin S Brink
- Department of Oral Health Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
- Department of Geological Sciences, University of Manitoba, 125 Dysart Road, Winnipeg, MB R3T 2N2, Canada
| | - Ping Wu
- Keck School of Medicine, University of Southern California, 2011 Zonal Ave, Los Angeles, CA HMR313, USA
| | - Cheng-Ming Chuong
- Keck School of Medicine, University of Southern California, 2011 Zonal Ave, Los Angeles, CA HMR313, USA
| | - Joy M Richman
- Department of Oral Health Sciences, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
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Haupaix N, Manceau M. The embryonic origin of periodic color patterns. Dev Biol 2020; 460:70-76. [DOI: 10.1016/j.ydbio.2019.08.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 08/02/2019] [Indexed: 01/29/2023]
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Abstract
One of the aims of developmental biology is to understand how a single egg cell gives rise to the complex spatial distributions of cell types and extracellular components of the adult phenotype. This review discusses the main genetic and epigenetic interactions known to play a role in tooth development and how they can be integrated into coherent models. Along the same lines, several hypotheses about aspects of tooth development that are currently not well understood are evaluated. This is done from their morphological consequences from the model and how these fit known morphological variation and change during tooth development. Thus the aim of this review is two-fold. On one hand the model and its comparison with experimental evidence will be used to outline our current understanding about tooth morphogenesis. On the other hand these same comparisons will be used to introduce a computational model that makes accurate predictions on three-dimensional morphology and patterns of gene expression by implementing cell signaling, proliferation and mechanical interactions between cells. In comparison with many other models of development this model includes reaction-diffusion-like dynamics confined to a diffusion chamber (the developing tooth) that changes in shape in three-dimensions over time. These changes are due to mechanical interactions between cells triggered by the proliferation enhancing effect of the reactants (growth factors). In general, tooth morphogenesis can be understood from the indirect cross-regulation between extracellular signals, the local regulation of proliferation and differentiation rates by these signals and the effect of intermediate developing morphology on the diffusion, dilution, and spatial distribution of these signals. Overall, this review should be interesting to either readers interested in the mechanistic bases of tooth morphogenesis, without necessarily being interested in modeling per se, and readers interested in development modeling in general.
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Affiliation(s)
- Isaac Salazar-Ciudad
- Developmental Biology Program, Institute of Biotechnology, P.O. Box 56, FIN-00014, University of Helsinki, Helsinki, Finland
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Abstract
In our paper we try to describe the basic concepts of chemical waves and spatial pattern formation in a simple way. We pay particular attention to self-organisation phenomena in extended excitable systems. These result in the appearance of travelling waves, spiral waves, target patterns, Turing structures or more complicated structures called scroll waves, which are three-dimensional systems. We describe the most famous oscillating reaction, the Belousov-Zhabotinsky (BZ) reaction, in greater detail. This is because it is of great interest in both physical chemistry and in studies on the evolution and sustenance of self-organising biological systems.
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Affiliation(s)
- Grazia Biosa
- Dipartimento di Chimica, Università di Sassari, Via Vienna 2, 07100 Sassari, Italy
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Trapani J. A morphometric analysis of polymorphism in the pharyngeal dentition of Cichlasoma minckleyi (Teleostei: Cichlidae). Arch Oral Biol 2004; 49:825-35. [PMID: 15308427 DOI: 10.1016/j.archoralbio.2004.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/10/2004] [Indexed: 10/26/2022]
Abstract
Dental polymorphism in teleost fishes often involves production of a robust dentition, or "molarization", in one morph. The lower pharyngeals of a sample of wild-caught individuals of the polymorphic Cuatro Cienegas cichlid, Cichlasoma minckleyi (Kornfield and Taylor) (Proc. Biol. Soc. Wash. 96 (1983) 253), were measured to investigate morphological changes associated with molarization. Principal components analysis demonstrates that dental variability in this species increases in larger fish, and that only the molariform morph contributes to this increase. Reduced major axis regression analyses between pairs of variables indicate that the papilliform morph increases both tooth measures and numbers, whereas the molariform morph maintains a relatively constant number of teeth as it produces teeth of progressively larger size. In the papilliform morph, negative allometric scaling between tooth size and dentigerous area is compensated for by addition of teeth. Tooth size variables are isometric in the molariform morph, and tooth numbers are nearly static. These results are consistent with those reported for other polymorphic cichlid species. Further study is required to elucidate the mechanisms whereby tooth form in polyphyodont species may respond to environmental factors (like food hardness), but possibilities include direct mechanical influences or transmission of signals via nerves to developing replacement teeth.
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Affiliation(s)
- Josh Trapani
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder 80309-0334, USA.
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Abstract
I propose that the labyrinthine patterns of the cortices of mammalian brains may be formed by a Turing instability of interacting axonal guidance species acting together with the mechanical strain imposed by the interconnecting axons.
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Affiliation(s)
- Julyan H E Cartwright
- Laboratorio de Estudios Cristalográficos, CSIC, Facultad de Ciencias, Campus Fuentenueva, Granada, Spain.
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